The death toll from forest fires that raged through seaside resorts near the Greek capital has increased to 74.

Fire service spokeswoman Stavroula Malliri said that a further 164 adults and 23 children are still being treated in hospitals for injuries after the fires broke out near Athens.

One of the fires began to the west of Athens near the town of Kineta, with another starting to the north-east near the port of Rafina – the latter seeing the worst of the casualties.

Both fires were fanned by gale-force winds that hampered firefighting efforts and sent hundreds of people fleeing to beaches, where they were evacuated by boat late at night.

Twenty-six of the dead were groups of families or friends found huddled together in Mati, near Rafina. Others swam out to sea to escape the inferno and some never came back.

Burned-out cars destroyed in the wildfires line a road near the village of Neos Voutzas (AP)

Greece endures wildfires every year but the fires that broke out on Monday were the deadliest to hit the country in decades. Fuelled by gale-force winds, they trapped thousands of people on beaches, roads and in homes.

Prime Minister Alexis Tsipras declared three days of national mourning for those killed as officials feared the death toll could rise even further, as there is no definitive count of how many people are missing.

Coast guard boats patrolled the shores near fire-hit areas after more than 700 people trapped by quick-moving fires had to be rescued from beaches or the sea, where six of the dead were found.

A crane removes a burned car from the road in Mati, east of Athens (AP)

While Greek authorities urged the public to contact them if they were looking for loved ones, many people took to social media, posting pictures of those they were looking for and their last known location before the fires struck.

Of the injured adults, 71 remain in hospital on Tuesday afternoon, with 10 of them in serious condition, while 11 of the children also remain in hospital.

Twenty-six of the dead were found at first light on Tuesday huddled together in one holiday compound near the sea in the community of Mati, near the port of Rafina. Red Cross rescuers who found them said they appeared to be families or groups of friends, as they were found hugging in groups of three and four.

Although the fires had largely abated by Tuesday afternoon, they were far from out.

Firefighters, aided by water-dropping aircraft from the sky, are tackling the remaining areas in the two main blazes near the capital.

Fires continued to burn in other parts of the country too, with one on the island of Crete the most severe.

With the flames whipped up by gale-force winds that frequently changed direction, many tourists and residents fled toward the coastline. Some swam out to sea, braving rough water and strong currents to escape the ferocious flames and choking smoke.

Scenes of devastation after the fire (AP)

The speed of the fire’s advance took many by surprise.

A flotilla of coast guard and private boats evacuated more than 700 people from threatened beaches overnight, authorities said. Defence minister Panos Kammenos said 88 people had been picked up from the sea by a military vessel.

Evangelos Bournous, the mayor of Rafina, blamed the high winds for the tragedy.

A woman stands amid the charred remains of burned-out properties in Mati (AP)

“We were unlucky,” he said. “The wind changed and it came at us with such force that it razed the coastal area in minutes.”

Rafina’s dock became a makeshift hospital during the night as paramedics checked survivors, some clad in only their bathing suits, who emerged from coast guard vessels and private boats.

In all, 47 brush and forest fires broke out across Greece on Monday and early Tuesday, with most of them quickly extinguished, the fire department said.

Greece sought international help through the European Union. Spain is sending two firefighting aircraft while Cyprus sent in 60 firefighters. Israel, Turkey and Bulgaria have also offered assistance.

Heavy rain is forecast across southern Greece on Wednesday, which it is hoped will boost the firefighting effort.